Organic light emitting diode and organic light emitting display device using the same

ABSTRACT

An organic light emitting diode and an organic light emitting display apparatus using the organic light emitting diode are provided. The organic light emitting diode includes a first electrode; a second electrode; and an organic layer between the first electrode and the second electrode to emit white light, and the organic layer is configured to emit white light in which an X-axis coordinate value in a color coordinate system is equal to or greater than 0.29, a Y-axis coordinate value in the color coordinate system is in a range of 0.32 to 0.45, and the Y-axis coordinate value in the color coordinate system is equal to or greater than the X-axis coordinate value in the color coordinate system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/885,542 filed Oct. 16, 2015, and claims thebenefit of the Korean Patent Application No. 10-2014-0165338 filed onNov. 25, 2014, which is hereby incorporated by reference for allpurposes as if fully set forth herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an organic light emitting diode. Moreparticularly, the present invention relates to an organic light emittingdiode that emits white light.

Discussion of the Related Art

An organic light emitting diode has a structure in which alight-emitting layer is formed between a cathode injecting electrons andan anode injecting holes. The electrons generated from the cathode andthe holes generated from the anode are injected into the light-emittinglayer, and the injected electrons and holes are combined to generateexcitons. The generated excitons transition from an excited state to aground state to emit light.

Such an organic light emitting diode can be variously applied to anillumination, a thin light source of a liquid crystal display apparatus,a display apparatus, and the like. Particularly, the organic lightemitting diode emitting white light can be applied to a full-colordisplay apparatus in combination with a color filter.

The organic light emitting diode emitting white light may include alight-emitting portion emitting blue light and a light-emitting portionemitting yellow-green light. In this case, the blue light and theyellow-green light emitted from the light-emitting portions are combinedand white light is finally emitted.

Hereinafter, an organic light emitting diode according to the relatedart will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of an organic light emittingdiode according to the related art.

As can be seen from FIG. 1, the organic light emitting diode accordingto the related art includes a first electrode 1, a first light-emittingportion 2, a second light-emitting portion 3, a third light-emittingportion 4, and a second electrode.

The first electrode 1 may function as an anode.

The first light-emitting portion 2 is formed on the first electrode 1and is configured to emit blue light. The first light-emitting portion 2includes a hole transporting layer, an electron transporting layer, anda blue light-emitting layer between the hole transporting layer and theelectron transporting layer.

The second light-emitting portion 3 is formed on the firstlight-emitting portion 2 and is configured to emit yellow-green light.The second light-emitting portion 3 includes a hole transporting layer,an electron transporting layer, and a yellow-green light-emitting layerbetween the hole transporting layer and the electron transporting layer.

The third light-emitting portion 4 is formed on the secondlight-emitting portion 3 and is configured to emit blue light. The thirdlight-emitting portion 4 includes a hole transporting layer, an electrontransporting layer, and a blue light-emitting layer between the holetransporting layer and the electron transporting layer.

The second electrode 5 is formed on the third light-emitting portion 4and may function as a cathode.

In the organic light emitting diode according to the related art, bluelight emitted from blue light-emitting layers in the firstlight-emitting portion 2 and the third light-emitting portion 4 andyellow-green light emitted from a yellow-green light-emitting layer inthe second light-emitting portion 3 are combined and white light isemitted. In general, the emission efficiency of blue light is lower thanthe emission efficiency of yellow-green light. Accordingly, twolight-emitting portions of the first light-emitting portion 2 and thethird light-emitting portion 4 include the blue light-emitting layer.

However, the organic light emitting diode according to the related arthas a problem with a color defect in which color coordinates of whitelight fluctuate depending on individual pixel positions and uniformwhite light is not emitted from the entire screen. This problem will bemore specifically described below with reference to FIG. 2.

FIG. 2 is a graph illustrating color coordinate values of white light bypixel positions in the organic light emitting diode according to therelated art.

In FIG. 2, the horizontal axis represents the pixel position and thevertical axis represents the color coordinate value. FIG. 2 illustratesX-axis color coordinate values and Y-axis color coordinate values ofwhite light which are measured at a total of fifteen pixel positionsfrom the left to the right of a screen.

As illustrated in FIG. 2, it can be seen that the X-axis colorcoordinate value and the Y-axis color coordinate value are not constantbut fluctuate depending on the pixel positions. Particularly, at somepixel positions, for example, at the fourth and thirteenth pixelpositions, the X-axis color coordinate value is almost equal to theY-axis color coordinate value. At the third pixel position, the X-axiscolor coordinate value is greater than the Y-axis color coordinatevalue. When the X-axis color coordinate value increases in the colorcoordinate system in this way, the emitted white light becomes reddish.As a result, since reddish white light is emitted from only some pixelpositions of the entire screen in the related art, there is a problem inthat image quality is lowered.

SUMMARY OF THE INVENTION

The present invention is made to solve the above-mentioned problems andan object thereof is to provide an organic light emitting diode whichcan improve image quality by solving the problem that reddish whitelight is emitted from only a specific pixel position and an organiclight emitting display apparatus including the organic light emittingdiode.

In order to achieve the above-mentioned object, an aspect of the presentinvention provides an organic light emitting diode including: a firstelectrode; a second electrode; and an organic layer between the firstelectrode and the second electrode to emit white light, wherein theorganic layer is configured to emit white light in which an X-axiscoordinate value in a color coordinate system is equal to or greaterthan 0.29, a Y-axis coordinate value in the color coordinate system isin a range of 0.32 to 0.45, and the Y-axis coordinate value in the colorcoordinate system is equal to or greater than the X-axis coordinatevalue in the color coordinate system.

The organic layer may be configured to emit white light in which theY-axis coordinate value in the color coordinate system is greater by0.03 or more than the X-axis coordinate value in the color coordinatesystem.

A range of fluctuation of the X-axis coordinate value at each pixelposition and a range of fluctuation of the Y-axis coordinate value ateach pixel position may be equal to or less than 0.015.

The organic layer may include a first light-emitting portion on thefirst electrode to emit blue light, a second light-emitting portion onthe first light-emitting portion to emit yellow-green light or mixedlight of green and red, and a third light-emitting portion on the secondlight-emitting portion to emit blue light.

The second light-emitting portion may include a lower light-emittinglayer and an upper light-emitting layer and a first distance from thetop surface of the first electrode to an interface between the lowerlight-emitting layer and the upper light-emitting layer may be equal toor less than a second distance from the bottom surface of the secondelectrode to the interface between the lower light-emitting layer andthe upper light-emitting layer.

A ratio of the second distance to the first distance may be in a rangeof 1.0 to 1.3.

The lower light-emitting layer and the upper light-emitting layer may beconfigured to emit yellow-green light and a concentration of a dopantwith which the lower light-emitting layer is doped may be greater than aconcentration of a dopant with which the upper light-emitting layer isdoped.

The lower light-emitting layer may be configured to emit red light andthe upper light-emitting layer may be configured to emit green light.

The first electrode may be a transflective electrode and the secondelectrode may be a reflective electrode.

Another aspect of the present invention provides an organic lightemitting display apparatus including: a substrate; a thin-filmtransistor layer on the substrate; an organic light emitting diode onthe thin-film transistor layer to emit white light; an encapsulationlayer on the organic light emitting diode; and a color filter layertransmitting light of a specific wavelength among the white lightemitted from the organic light emitting diode, wherein the organic lightemitting diode includes a first electrode, a second electrode, and anorganic layer between the first electrode and the second electrode toemit white light and wherein the organic layer is configured to emitwhite light in which an X-axis coordinate value in a color coordinatesystem is equal to or greater than 0.29, a Y-axis coordinate value inthe color coordinate system is in a range of 0.32 to 0.45, and theY-axis coordinate value in the color coordinate system is equal to orgreater than the X-axis coordinate value in the color coordinate system.

The organic layer may be configured to emit white light in which theY-axis coordinate value in the color coordinate system is greater by0.03 or more than the X-axis coordinate value in the color coordinatesystem.

A range of fluctuation of the X-axis coordinate value at each pixelposition and a range of fluctuation of the Y-axis coordinate value ateach pixel position may be equal to or less than 0.015.

The organic layer may include a first light-emitting portion on thefirst electrode to emit blue light, a second light-emitting portion onthe first light-emitting portion to emit yellow-green light or mixedlight of green and red, and a third light-emitting portion on the secondlight-emitting portion to emit blue light.

The second light-emitting portion may include a lower light-emittinglayer and an upper light-emitting layer and a first distance from thetop surface of the first electrode to an interface between the lowerlight-emitting layer and the upper light-emitting layer may be equal toor less than a second distance from the bottom surface of the secondelectrode to the interface between the lower light-emitting layer andthe upper light-emitting layer.

A ratio of the second distance to the first distance may be in a rangeof 1.0 to 1.3.

Another aspect of the present invention provides an organiclight-emitting display apparatus including: a first electrode; a secondelectrode; a first light-emitting portion on the first electrode, thefirst light-emitting portion including a first light-emitting layer; asecond light-emitting portion on the first light-emitting portion, thesecond light-emitting portion including a second light-emitting layer;and a third light-emitting portion on the second light-emitting portion,the third light-emitting portion including a third light-emitting layer,wherein the second light-emitting layer includes a first area and asecond area, and a first distance from the top surface of the firstelectrode to the first area is equal to or less than a second distancefrom the bottom surface of the second electrode to the second area.

A ratio of the second distance to the first distance may be in a rangeof 1.0 to 1.3.

The second light-emitting layer may be configured to emit yellow-greenlight and a concentration of a dopant with which the first area is dopedmay be greater than a concentration of a dopant with which the secondarea is doped so as to enhance red efficiency.

White light in which an X-axis coordinate value in a color coordinatesystem is equal to or greater than 0.29, a Y-axis coordinate value inthe color coordinate system is in a range of 0.32 to 0.45, and theY-axis coordinate value in the color coordinate system is equal to orgreater than the X-axis coordinate value in the color coordinate systemmay be emitted so as to reduce a color defect of the organic lightemitting display apparatus.

A range of fluctuation of the X-axis coordinate value at each pixelposition and a range of fluctuation of the Y-axis coordinate value ateach pixel position may be equal to or less than 0.015 so as to minimizea color coordinate difference of the white light at each pixel positionof the organic light-emitting display apparatus.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a schematic cross-sectional view of an organic light emittingdiode according to the related art;

FIG. 2 is a graph illustrating color coordinate values of white light atpixel positions in the organic light emitting diode according to therelated art;

FIG. 3 is a graph illustrating a color coordinate system of an organiclight emitting diode according to an embodiment of the presentinvention;

FIG. 4 is a graph illustrating color coordinate values of white light atpixel positions in the organic light emitting diode according to theembodiment of the present invention;

FIG. 5 is a schematic cross-sectional view of the organic light emittingdiode according to the embodiment of the present invention;

FIG. 6 is a diagram illustrating positions of peak wavelengths in theorganic light emitting diode by wavelengths of blue light andyellow-green (YG) light; and

FIG. 7 is a schematic cross-sectional view of an organic light emittingdisplay apparatus according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Advantages and features of the invention and methods for achieving theadvantages or features will be apparent from embodiments described belowin detail with reference to the accompanying drawings. However, theinvention is not limited to the embodiments but can be modified invarious forms. The embodiments are provided merely for completing thedisclosure of the invention and are provided for completely informingthose skilled in the art of the scope of the invention. The scope of theinvention is defined by only the appended claims.

Shapes, sizes, ratios, angles, number of pieces, and the likeillustrated in the drawings, which are provided for the purpose ofexplaining the embodiments of the invention, are exemplary and thus theinvention is not limited to the illustrated details. In the followingdescription, like elements are referenced by like reference numerals.When it is determined that detailed description of the relevant knownfunctions or configurations involved in the invention makes the gist ofthe invention obscure, the detailed description thereof will not bemade. When “include,” “have”, “be constituted”, and the like arementioned in the specification, another element may be added unless“only” is used. A singular expression of an element includes two or moreelements unless differently mentioned.

In construing elements, an error range is included even when explicitdescription is not made.

For example, when positional relationships between two parts aredescribed using ‘on˜’, ‘over˜’, ‘under˜’, ‘next˜’, and the like, one ormore other parts may be disposed between the two parts unless ‘just’ or‘direct’ is used.

For example, when temporal relationships are described using “after”,“subsequent to”, “next”, “before”, and the like, such expression mayinclude temporal discontinuity unless “immediately” or “directly” isused.

Terms “first”, “second”, and the like can be used to describe variouselements, but the elements should not be limited to the terms. The termsare used only to distinguish an element from another. Therefore, a firstelement may be a second element within the technical spirit of theinvention.

Features of the embodiments of the invention can be coupled or combinedpartially or on the whole and can be technically interlinked and drivenin various forms. The embodiments may be put into practice independentlyor in combination.

Hereinafter, embodiments of the invention will be described in detailwith reference to the accompanying drawings.

FIG. 3 is a graph illustrating a color coordinate system of an organiclight emitting diode according to an embodiment of the present inventionand specifically illustrates a CIE color coordinate system. Colorcoordinates in the entire specification mean CIE color coordinates.

An organic light emitting diode according to an embodiment of theinvention emits white light. Such white light satisfies the followingconditions.

First, white light emitted from the organic light emitting diodeaccording to the embodiment of the invention satisfies conditions thatan X-axis coordinate value in the color coordinate system is equal to orgreater than 0.29 and a Y-axis coordinate value in the color coordinatesystem is in a range of 0.32 to 0.45.

When the X-axis coordinate value of the emitted light is equal to orgreater than 0.29 and the Y-axis coordinate value thereof is in a rangeof 0.32 to 0.45, light having color coordinate values in the rectangularrange (see A) in FIG. 3 is emitted. The light having the colorcoordinate values in the rectangular range (see A) includes reddishwhite light to red light. Accordingly, red light should be removed fromthe rectangular range (see A) so as to acquire white light.

In the white light emitted from the organic light emitting diodeaccording to the embodiment of the invention, the Y-axis coordinatevalue in the color coordinate system is equal to or greater than theX-axis coordinate value in the color coordinate system. As describedabove, when the X-axis coordinate value is equal to or greater than0.29, the Y-axis coordinate value in the color coordinate system is in arange of 0.32 to 0.45, and the Y-axis coordinate value in the colorcoordinate system is equal to or greater than the X-axis coordinatevalue in the color coordinate system, light having color coordinatevalues in a relatively-large triangular range (see B) is emitted in FIG.3. The light having the color coordinate values in the relatively-largetriangular range (see B) corresponds to reddish white light.

As a result, according to the embodiment of the invention, the emittedlight corresponds to reddish white light. Therefore, even when theX-axis color coordinate value and the Y-axis color coordinate value ateach pixel position are not constant but fluctuate and reddish whitelight is emitted from a specific pixel position, reddish white light isalready emitted from the screen as a whole and thus a user cannotrecognize a color defect at the specific pixel position.

In the embodiment of the invention, when the X-axis coordinate value inthe color coordinate system is less than 0.29, the emitted light may bebluish and desired reddish white light may not be acquired. When theY-axis coordinate value in the color coordinate system is less than 0.32or greater than 0.45, the emitted light may deviate from a colorcoordinate range of white light. Accordingly, in order to acquiredesired white light, it is preferable that the X-axis coordinate valuein the color coordinate system may be equal to or greater than 0.29 andthe Y-axis coordinate value in the color coordinate system may be in therange of 0.32 to 0.45.

On the other hand, when a concentration of red is high in emittingreddish white light form the entire screen, image quality may beadversely affected and it is thus necessary to appropriately adjust theconcentration of red in the white light. Accordingly, in white lightemitted from an organic light emitting diode according to anotherembodiment of the invention, the Y-axis coordinate value in the colorcoordinate system is greater by 0.03 or more than the X-axis coordinatevalue.

As described above, when the X-axis coordinate value in the colorcoordinate system is equal to or greater than 0.29, the Y-axiscoordinate value in the color coordinate system is in a range of 0.32 to0.45, and the Y-axis coordinate value in the color coordinate system isgreater by 0.03 or more than the X-axis coordinate value in the colorcoordinate system, light having color coordinate values in therelatively-small triangular range (see C) in FIG. 3 is emitted. Sincethe light having the color coordinate values in the relatively-smalltriangular range (see C) is not higher in the concentration of red thanthe light having the color coordinate values in the relatively-largetriangular range (see B), the image quality can be improved.

FIG. 4 is a graph illustrating color coordinate values of white light atpixel positions in the organic light emitting diode according to theembodiment of the invention. In FIG. 4, the horizontal axis representsthe pixel position and the vertical axis represents the color coordinatevalue.

As illustrated in FIG. 4, in the white light emitted from the organiclight emitting diode according to the embodiment of the invention, theX-axis coordinate value in the color coordinate system is equal to orgreater than 0.29, the Y-axis coordinate value in the color coordinatesystem is in a range of 0.32 to 0.45, and the Y-axis coordinate value inthe color coordinate system is equal to or greater than the X-axiscoordinate value in the color coordinate system.

On the other hand, the X-axis color coordinate value and the Y-axiscolor coordinate value at each pixel position are not constant but mayfluctuate. At this time, it is preferable that the range of fluctuationΔX of the X-axis coordinate value of white light at each pixel positionbe equal to or less than 0.015 and the range of fluctuation ΔY of theY-axis coordinate value of white light at each pixel position be equalto or less than 0.015. When the range of fluctuation ΔX of the X-axiscoordinate value or the range of fluctuation ΔY of the Y-axis coordinatevalue is greater than 0.015, there is a possibility that the colorcoordinate difference of white light at each pixel position willincrease and the image quality will be lowered.

According to the invention, reddish white light is emitted by adjustingthe emitted light such that the X-axis coordinate value in the colorcoordinate system is equal to or greater than 0.29, the Y-axiscoordinate value in the color coordinate system is in a range of 0.32 to0.45, and the Y-axis coordinate value in the color coordinate system isequal to or greater than the X-axis coordinate value in the colorcoordinate system or is greater by 0.03 or more the X-axis coordinatevalue. This can be implemented by adjusting the position of a secondlight-emitting layer in a second light-emitting portion located in themiddle of the organic light emitting diode having plural light-emittingportions as will be described later.

FIG. 5 is a schematic cross-sectional view of the organic light emittingdiode according to the embodiment of the invention.

As illustrated in FIG. 5, the organic light emitting diode according tothe embodiment of the invention includes a first electrode 100, a firstlight-emitting portion 200, a first charge generating layer 300, asecond light-emitting portion 400, a second charge generating layer 500,a third light-emitting portion 600, and a second electrode 700.

The first electrode 100 can function as an anode. The first electrode100 can be formed of a transparent conductive material having a highconductivity and a high work function, such as indium tin oxide (ITO),indium zinc oxide (IZO), SnO2, or ZnO, but is not limited to thematerial.

The first light-emitting portion 200 is formed on the first electrode100 and emits blue light. The first light-emitting portion 200 includesa hole injecting layer 210, a first hole transporting layer 220, a firstlight-emitting layer 230, and a first electron transporting layer 240.

The hole injecting layer 210 is formed on the first electrode 100 andcan be formed ofMTDATA(4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine),CuPc(copper phthalocyanine), PEDOT/PSS(poly(3,4-ethylenedioxythiphene,polystyrene sulfonate), or the like, but is not limited to thesematerials. For example, the hole injecting layer 210 may be formed bydoping a material constituting the first hole transporting layer 220with a P-type dopant.

The first hole transporting layer 220 is formed on the hole injectinglayer 210 and can be formed ofTPD(N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-bi-phenyl-4,4′-diamine),NPD(N, N-dinaphthyl-N, N′-diphenyl benzidine),NPB(N,N′-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine), or the like, butis not limited to these materials. The first hole transporting layer 220may be formed of the same material as the hole injecting layer 210except that the first hole transporting layer 220 is not doped with theP-type dopant. In this case, the hole injecting layer 210 and the firsthole transporting layer 220 may be formed through a continuousdeposition process using the same processing equipment.

The first light-emitting layer 230 is formed on the first holetransporting layer 220. The first light-emitting layer 230 is formed ofa blue light-emitting layer emitting blue light.

The first light-emitting layer 230 may include, for example, an organicmaterial capable of emitting blue light of which a peak wavelengthranges from 440 nm to 480 nm. The first light-emitting layer may beformed by doping at least one fluorescent host material among anthracenederivatives, pyrene derivatives, and perylene derivatives with afluorescent blue dopant, but is not limited to this example.

The first electron transporting layer 240 is formed on the firstlight-emitting layer 230 and can be formed of oxadiazole, triazole,phenanthroline, benzoxazole, benzthiazole, or the like, but is notlimited to these materials.

The first charge generating layer 300 is formed between the firstlight-emitting portion 200 and the second light-emitting portion 400 andfunctions to harmoniously adjust charges between the firstlight-emitting portion 200 and the second light-emitting portion 400.The first charge generating layer 300 includes an n-type chargegenerating layer formed on the first light-emitting portion 200 andlocated adjacent to the first light-emitting portion 200 and a p-typecharge generating layer formed on the n-type charge generating layer andlocated adjacent to the second light-emitting portion 400. The n-typecharge generating layer injects electrons into the first light-emittingportion 200 and the p-type charge generating layer injects holes intothe second light-emitting portion 400. The n-type charge generatinglayer can be formed of an organic layer doped with an alkali metal suchas Li, Na, K, or Cs or an alkali earth metal such as Mg, Sr, Ba, or Ra.The p-type charge generating layer can be formed by doping an organicmaterial having hole transporting capability with a dopant.

The second light-emitting portion 400 is formed on the first chargegenerating layer 300 and can emit yellow-green light or mixed light ofgreen and red. The second light-emitting portion 400 includes a secondhole transporting layer 420, a second light-emitting layer 430, and asecond electron transporting layer 440.

The second hole transporting layer 420 is formed on the first chargegenerating layer 300 and can be formed ofTPD(N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-bi-phenyl-4,4′-diamine),NPD(N, N-dinaphthyl-N, N′-diphenyl benzidine),NPB(N,N′-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine), or the like, butis not limited to these materials. The second hole transporting layer420 can be formed of the same material as the first hole transportinglayer 220, but may be formed of a material different therefrom in somecases.

The second light-emitting layer 430 is formed on the second holetransporting layer 420. The second light-emitting layer 430 includes alower light-emitting layer 431 and an upper light-emitting layer 432.

Both the lower light-emitting layer 431 and the upper light-emittinglayer 432 can be formed of a yellow-green light-emitting layer emittingyellow-green light. In this case, the lower light-emitting layer 431 andthe upper light-emitting layer 432 can include an organic materialcapable of emitting yellow-green light, for example, light of which thepeak wavelength ranges from 520 nm to 590 nm, and can be specificallyformed by doping a phosphorescent host material includingcarbazole-based compound or metal complex with a phosphorescentyellow-green dopant. Examples of the carbazole-based compound includeCBP(4,4-N,N′-dicarbazole-biphenyl), CBP derivatives,mCP(N,N′-dicarbazolyl-3,5-benzene), and mCP derivatives. Examples of themetal complex include ZnPBO(phenyloxazole) metal complex andZnPBT(phenylthiazole) metal complex.

When the lower light-emitting layer 431 and the upper light-emittinglayer 432 are formed of the yellow-green light-emitting layer, theconcentration of the dopant of the lower light-emitting layer 431 ispreferably higher than the concentration of the dopant of the upperlight-emitting layer 432. According to the embodiment of the invention,by adjusting the concentration of the dopant in the lower light-emittinglayer 431 close to the first electrode 100 functioning as an anode to behigher than the concentration of the dopant in the upper light-emittinglayer 432 distant from the first electrode 100, it is possible toimprove emission efficiency of the light emitted from the lowerlight-emitting layer 431 having a relatively-high concentration of adopant, which is advantageous for emission of reddish white light. Thiswill be described later.

On the other hand, according to another embodiment of the invention, thelower light-emitting layer 431 is formed of a red light-emitting layeremitting red light and the upper light-emitting layer 432 is formed of agreen light-emitting layer emitting green light. In this case, the lowerlight-emitting layer 431 can include an organic material capable ofemitting red light, for example, light of which the peak wavelengthranges from 600 nm to 650 nm, and can be specifically formed by doping aphosphorescent host material including carbazole-based compound or metalcomplex with a red dopant such as metal complex of Ir or Pt. The upperlight-emitting layer 432 can include an organic material capable ofemitting green light, for example, light of which the peak wavelengthranges from 540 nm to 590 nm, and can be specifically formed by doping aphosphorescent host material including carbazole-based compound or metalcomplex with a green dopant. According to the embodiment of theinvention, by forming the lower light-emitting layer 431 close to thefirst electrode 100 functioning as an anode out of the redlight-emitting layer and forming the upper light-emitting layer 432distant from the first electrode 100 out of the green light-emittinglayer, it is possible to improve emission efficiency of the lightemitted from the lower light-emitting layer 431 formed of the redlight-emitting layer, which is advantageous for emission of reddishwhite light. This will be described later.

The second electron transporting layer 440 is formed on the secondlight-emitting layer 430 and can be formed of oxadiazole, triazole,phenanthroline, benzoxazole, benzthiazole, or the like, but is notlimited to these materials. The second electron transporting layer 440can be formed of the same material as the first electron transportinglayer 240, but may be formed of a material different therefrom in somecases.

The second charge generating layer 500 is formed between the secondlight-emitting portion 400 and the third light-emitting portion 600 andfunctions to harmoniously adjust charges between the secondlight-emitting portion 400 and the third light-emitting portion 600. Thesecond charge generating layer 500 includes an n-type charge generatinglayer formed on the second light-emitting portion 400 and locatedadjacent to the second light-emitting portion 400 and a p-type chargegenerating layer formed on the n-type charge generating layer andlocated adjacent to the third light-emitting portion 600. The n-typecharge generating layer and the p-type charge generating layer can beformed of the same materials as the first charge generating layer 300.

The third light-emitting portion 600 is formed on the second chargegenerating layer 500 and can emit blue light. The third light-emittingportion 600 includes a third hole transporting layer 620, a thirdlight-emitting layer 630, a third electron transporting layer 640, andan electron injecting layer 650.

The third hole transporting layer 620 is formed on the second chargegenerating layer 500 and can be formed ofTPD(N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-bi-phenyl-4,4′-diamine),NPD(N, N-dinaphthyl-N, N′-diphenyl benzidine),NPB(N,N′-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine), or the like, butis not limited to these materials. The third hole transporting layer 620can be formed of the same material as the first hole transporting layer220 or the second hole transporting layer 420, but may be formed of amaterial different therefrom in some cases.

The third light-emitting layer 630 is formed on the third holetransporting layer 620. The third light-emitting layer 630 includes ablue light-emitting layer emitting blue light.

The blue light-emitting layer may include, for example, an organicmaterial capable of emitting blue light, for example, blue light ofwhich the peak wavelength ranges from 440 nm to 480 nm and can be formedspecifically by doping at least one fluorescent host material amonganthracene derivatives, pyrene derivatives, and perylene derivativeswith a fluorescent blue dopant, but is not limited to this example.

The third light-emitting layer 630 can be formed of the same material asthe first light-emitting layer 230, but may be formed of a materialdifferent therefrom in some cases.

The third electron transporting layer 640 is formed on the thirdlight-emitting layer 630 and can be formed of oxadiazole, triazole,phenanthroline, benzoxazole, benzthiazole, or the like, but is notlimited to these materials. The third electron transporting layer 640can be formed of the same material as the first electron transportinglayer 240 or the second electron transporting layer 440, but may beformed of a material different therefrom in some cases.

The electron injecting layer 650 is formed on the third electrontransporting layer 640 and can be formed of lithium fluoride (LiF) orlithium quinolate (Liq), but is not limited to these materials.

The second electrode 700 is formed on the third light-emitting portion600. The second electrode 700 can function as a cathode. The secondelectrode 700 can be formed of a metal having a low work function, suchas aluminum (Al), silver (Ag), magnesium (Mg), lithium (Li), or calcium(Ca), but is not limited to these materials.

According to the above-mentioned embodiment of the invention, the firstlight-emitting layer 230 in the first light-emitting portion 200 and thethird light-emitting layer 630 in the third light-emitting portion 600emit blue light, and the second light-emitting layer 430 in the secondlight-emitting portion 400 emits yellow-green light or mixed light ofgreen (G) and red (R), whereby white light can be emitted.

On the other hand, the second electrode 700 can function as a reflectiveelectrode which is opaque to reflect light, and the first electrode 100can function as a transflective electrode which is translucent totransmit some light and to reflect some light. In this case, it ispossible to obtain improvement in emission efficiency due to microcavityoccurring between the first electrode 100 and the second electrode 700.The microcavity means that light is repeatedly reflected andre-reflected to cause constructive interference between the firstelectrode 100 and the second electrode 700 which are separated by anoptical path length from each other and the finally-emitted light isamplified to improve the emission efficiency. At this time, in order forlight to be repeatedly reflected and re-reflected to cause theconstructive interference, a resonance distance for each wavelength ofemitted light should be set between the first electrode 100 and thesecond electrode 700. The resonance distance has to be designed to be aninteger multiple of a half wavelength (λ/2) of the emitted light.

When the resonance distance for light of a specific wavelength is formedin this way, light of the corresponding wavelength among the emittedlight is repeatedly reflected between the first electrode 100 and thesecond electrode 700 and is emitted to the outside in a state in whichthe amplitude of the light has increased due to the constructiveinterference. On the other hand, light of other wavelengths isrepeatedly reflected between the first electrode 100 and the secondelectrode 700 and is emitted to the outside in a state in which theamplitude of the light has decreased due to the destructiveinterference. Accordingly, the emission efficiency for light of thespecific wavelength corresponding to the resonance distance may beimproved by a microcavity effect

Here, the spectrum of the second light-emitting layer 430 moves to along wavelength range when the second light-emitting layer 430 isseparated apart from the second electrode 700, and moves to a shortwavelength range when the second light-emitting layer 430 approaches thesecond electrode 700. This is because the spectrum varies depending onthe optical path length when light emitted from the secondlight-emitting layer 430 is reflected by the second electrode 700 and isemitted to the second electrode 100. Accordingly, in order to improvethe emission efficiency using the microcavity, it is preferable that thesecond light-emitting layer 430 move to a long wavelength range. Thatis, it is preferable that the second light-emitting layer 430 be formedclose to the first electrode 100.

Since the second electrode 700 is a reflective electrode and the firstelectrode 100 is a transflective electrode, light is emitted through thefirst electrode 100. Accordingly, in order to acquire desired reddishwhite light, it is preferable that the second light-emitting layer 430emitting light of a long wavelength be located at a position closer tothe first second electrode 100 than the second electrode 700.

Preferably, a first distance L1 from the top surface of the firstelectrode 100 to an interface between the lower light-emitting layer 431and the upper light-emitting layer 432 of the second light-emittinglayer 430 is equal to or less than a second distance L2 from the bottomsurface of the second electrode 700 to the interface between the lowerlight-emitting layer 431 and the upper light-emitting layer 432 of thesecond light-emitting layer 430.

When the first distance L1 is equal to or less than the second distanceL2, the lower light-emitting layer 431 of the second light-emittinglayer 430 is located closer to the first electrode 100 than the secondelectrode 700. Accordingly, it is possible to obtain an effect ofimprovement in the emission efficiency of light emitted from the redlight-emitting layer constituting the lower light-emitting layer 431 orthe yellow-green light-emitting layer having a relatively-highconcentration of a dopant, which is advantageous for emitting reddishwhite light.

On the other hand, a ratio L2/L1 of the second distance L2 to the firstdistance L1 is preferably in a range of 1.0 to 1.3. When the ratio L2/L1of the second distance L2 to the first distance L1 is greater than 1.3,the lower light-emitting layer 431 of the second light-emitting layer430 may be located excessively close to the first electrode 100 and theeffect of improvement in the emission efficiency may not be achieved.

FIG. 6 is a diagram illustrating a peak wavelength position in theorganic light emitting diode for each wavelength of blue (B) light andyellow-green (YG) light.

In FIG. 6, the horizontal axis represents the wavelength (nm) of lightand the vertical axis represents the position in the thickness directionof the organic light-emitting device.

As illustrated in FIG. 6, the peak wavelength is present at a total offour positions (1), (2), (3), and (4) between the anode and the cathodein the blue wavelength band, that is, in a wavelength band between 440nm and 480 nm. Here, position (1) overlaps the anode and it is thusdifficult to form the blue light-emitting layer at that position.Position (3) may overlap the yellow-green (YG) light-emitting layer andit is thus difficult to form the blue light-emitting layer at thatposition. Therefore, it is preferable that the blue light-emitting layerbe formed at position (2) and position (4). That is, it is preferablethat the first light-emitting layer 230 emitting blue light in the firstlight-emitting portion 200 be located at position (2) and the thirdlight-emitting layer 630 emitting blue light in the third light-emittingportion 600 be located at position (4).

In the yellow-green (YG) wavelength band, that is, in the wavelengthband between 520 nm to 590 nm, the peak wavelength is present at a totalof three positions (1), (2), and (3) between the anode and the cathode.Here, in consideration of the positions of the first light-emittinglayer 230 and the third light-emitting layer 630 emitting blue light, itis preferable that the yellow-green (YG) light-emitting layer be formedat position (2). That is, it is preferable that the secondlight-emitting layer 430 of the second light-emitting portion 400 belocated at position (2).

Here, position (2) at which the second light-emitting layer 430 of thesecond light-emitting portion 400 is located corresponds to the areamarked by x between the anode and the cathode of the organic lightemitting diode. The middle point of the area marked by x corresponds tothe interface between the lower light-emitting layer 431 (YG1) and theupper light-emitting layer 432 (YG2) of the second light-emitting layer430. Accordingly, the distance from the anode to the middle point of thearea marked by x is the first distance L1 and the distance from thecathode to the middle point of the area marked by x is the seconddistance L2.

As an experiment result, the ratio L2/L1 of the second distance L2 tothe first distance L1 ranges from 1.0 to 1.3.

The organic light emitting diode according to the invention can beapplied to an illumination, may be used as a thin light source of aliquid crystal display apparatus, or may be applied to a displayapparatus. An example in which the organic light emitting diodeaccording to the invention is applied to a display apparatus will bedescribed below.

FIG. 7 is a schematic cross-sectional view of an organic light emittingdisplay apparatus according to an embodiment of the invention, where theorganic light emitting diode illustrated in FIG. 5 is used.

As illustrated in FIG. 7, the organic light emitting display apparatusaccording to an embodiment of the invention includes a substrate 10, athin-film transistor layer 20, a color filter layer 30, a planarizationlayer 40, a bank layer 50, a first electrode 100, an organic layer 1, asecond electrode 700, an encapsulation layer 60, and an encapsulationsubstrate 70.

The substrate 10 may be formed of glass or a flexible transparentplastic such as polyimide, but is not limited to these materials.

The thin-film transistor layer 20 is formed on the substrate 10. Thethin-film transistor layer 20 includes a gate electrode 21, a gateinsulating film 22, a semiconductor layer 23, a source electrode 24 a, adrain electrode 24 b, and a protective film 25.

The gate electrode 21 is formed in patterns on the substrate 10, thegate insulating film 22 is formed on the gate electrode 21, thesemiconductor layer 23 is formed on the gate insulating film 22, thesource electrode 24 a and the drain electrode 24 b are formed inpatterns on the semiconductor layer 23 so as to face each other, and theprotective film 25 is formed on the source electrode 24 a and the drainelectrode 24 b.

In the drawing, a bottom gate structure in which the gate electrode 21is formed under the semiconductor layer 23 is illustrated, but a topgate structure in which the gate electrode 21 is formed on thesemiconductor layer 23 may be employed.

The color filter layer 30 is formed on the thin-film transistor layer20. The color filter layer 30 includes a red (R) color filter, a green(G) color filter, and a blue (B) color filter which are formed inpatterns for each pixel. The color filter layer 30 transmits light of aspecific wavelength among white light emitted from the organic layer 1.

The planarization layer 40 is formed on the color filter layer 30 toplanarize the surface of the substrate. The planarization layer 40 canbe formed of an organic insulating film such as photoacryl, but is notlimited to the material.

The bank layer 50 is formed on the planarization layer 40 to definepixel areas. That is, the bank layer 50 is formed in a matrix structurein boundary areas between plural pixels, whereby the pixel areas aredefined by the bank layer 50.

The combination of the first electrode 100, the organic layer 1, and thesecond electrode 700 is the organic light emitting diode emittingreddish white light illustrated in FIG. 5.

The first electrode 100 is connected to the drain electrode 24 b viacontact holes formed in the protective film 25 and the planarizationlayer 40. The first electrode 100 is formed in patterns for each pixel.

The second electrode 700 is also formed on the bank layer 50 as well asthe organic layer 1. This is because a common voltage is applied to thesecond electrode 700 and it is thus necessary to form the secondelectrode in patterns for each pixel.

The organic layer 1 includes the first light-emitting layer 200, thefirst charge generating layer 300, the second light-emitting layer 400,the second charge generating layer 500, and the third light-emittingportion 600 and detailed description thereof will not be repeated.

The organic layer 1 is divided by pixels in the drawing, but is notlimited to this configuration. The organic layers 1 by pixels may beconnected to each other. According to an embodiment of the invention,white light is emitted from the organic layer 1 and the emitted whitelight passes through the color filter layer 30 formed in patterns foreach pixel to form a full color image. Accordingly, since the organiclayer 1 emitting the white light is commonly applied to all the pixels,the organic layer 1 may not be divided by pixels.

The encapsulation layer 60 is formed on the second electrode 700. Theencapsulation layer 60 functions to prevent moisture from permeating theorganic layer 1. The encapsulation layer 60 may include multiple layersin which different inorganic materials are stacked or multiple layers inwhich an inorganic material and an organic material are alternatelystacked.

The encapsulation substrate 70 is formed on the encapsulation layer 60.The encapsulation substrate 70 may be formed of glass or plastic or maybe formed of metal. The encapsulation substrate 70 may be attached tothe encapsulation layer 60 with an adhesive.

The organic light-emitting display apparatus illustrated in FIG. 7employs a so-called bottom emission type in which light emitted from theorganic layer 1 travels toward the substrate 10 on the downside, but theinvention is not limited to this type. A so-called top emission type inwhich light emitted from the organic layer 1 travels toward theencapsulation substrate 70 on the upside may be employed. When theinvention employs the top emission type, the color filter layer 30 maybe formed on the bottom surface of the encapsulation substrate 70.

According to an embodiment of the present invention, the organic layeremits reddish white light. Accordingly, even when the X-axis colorcoordinate value and the Y-axis color coordinate value at each pixelposition are not constant but fluctuate and reddish white light isemitted from a specific pixel position, reddish white light is alreadyemitted from the screen as a whole and thus a user cannot recognize acolor defect at the specific pixel position.

While the embodiments of the invention have been described above withreference to the accompanying drawings, the invention is not limited tothe embodiments, but can be modified in various forms without departingfrom the technical spirit of the invention. Therefore, theabove-mentioned embodiments of the invention are not provided fordefining the technical spirit of the invention but for explaining thetechnical spirit thereof, and the scope of the invention is not limitedto the embodiments. Accordingly, it should be understood that theabove-mentioned embodiments are exemplary in all the points of view andare not restrictive. It should be construed that the scope of theinvention is defined by only the appended claims and all technicalconcepts equivalent thereto are included in the scope of the invention.

What is claimed is:
 1. An organic light emitting display apparatus, comprising: a first electrode; a second electrode; and an organic layer between the first electrode and the second electrode to emit white light, wherein the organic layer includes a first light-emitting portion, a second light-emitting portion, and a third light-emitting portion, wherein the organic layer is configured to emit white light having an X-axis coordinate value and a Y-axis coordinate value in a color coordinate system, and wherein a range of fluctuation of the X-axis coordinate value at each pixel position and a range of fluctuation of the Y-axis coordinate value at each pixel position are equal to or less than 0.015.
 2. The apparatus of claim 1, wherein the Y-axis coordinate value in the color coordinate system is greater by 0.03 or more than the X-axis coordinate value in the color coordinate system.
 3. The apparatus of claim 1, wherein the X-axis coordinate value in a color coordinate system is equal to or greater than 0.29, and the Y-axis coordinate value in the color coordinate system is in a range of 0.32 to 0.45.
 4. The apparatus of claim 1, wherein the first light-emitting portion is disposed on the first electrode to emit blue light, the second light-emitting portion is disposed on the first light-emitting portion to emit yellow-green light or mixed light of green and red, and the third light-emitting portion is disposed on the second light-emitting portion to emit blue light.
 5. The apparatus of claim 4, wherein the second light-emitting portion is configured to emit the green and red light, and the second light-emitting portion includes a lower light-emitting layer to emit the red light and an upper light-emitting layer to emit the green light.
 6. The apparatus of claim 1, wherein the second light-emitting portion is configured to emit the yellow-green light, and the second light-emitting portion includes a lower light-emitting layer and an upper light-emitting layer.
 7. The apparatus of claim 6, wherein a concentration of a dopant of the lower light-emitting layer is greater than a concentration of a dopant of the upper light-emitting layer.
 8. The apparatus of claim 1, wherein the second light-emitting portion includes a lower light-emitting layer and an upper light-emitting layer, and a first distance from a top surface of the first electrode to an interface between the lower light-emitting layer and the upper light-emitting layer is equal to or less than a second distance from a bottom surface of the second electrode to the interface between the lower light-emitting layer and the upper light-emitting layer.
 9. The apparatus of claim 8, wherein a ratio of the second distance to the first distance is in a range of 1.0 to 1.3.
 10. The apparatus of claim 1, wherein the first electrode is a transflective electrode and the second electrode is a reflective electrode.
 11. An organic light emitting display apparatus, comprising: a first electrode; a second electrode; and an organic layer between the first electrode and the second electrode to emit white light, wherein the organic layer includes a first light-emitting portion, a second light-emitting portion, and a third light-emitting portion, wherein the organic layer is configured to emit white light having an X-axis coordinate value and a Y-axis coordinate value in a color coordinate system, and wherein the second light-emitting portion includes a lower light-emitting layer and an upper light-emitting layer, a concentration of a dopant of the lower light-emitting layer being greater than a concentration of a dopant of the upper light-emitting layer.
 12. The apparatus of claim 11, wherein the Y-axis coordinate value in the color coordinate system is greater by 0.03 or more than the X-axis coordinate value in the color coordinate system.
 13. The apparatus of claim 11, wherein the X-axis coordinate value in a color coordinate system is equal to or greater than 0.29, and the Y-axis coordinate value in the color coordinate system is in a range of 0.32 to 0.45.
 14. The apparatus of claim 11, wherein a range of fluctuation of the X-axis coordinate value at each pixel position and a range of fluctuation of the Y-axis coordinate value at each pixel position are equal to or less than 0.015.
 15. The apparatus of claim 11, wherein the first light-emitting portion is disposed on the first electrode to emit blue light, the second light-emitting portion is disposed on the first light-emitting portion to emit yellow-green light or mixed light of green and red, and the third light-emitting portion is disposed on the second light-emitting portion to emit blue light.
 16. The apparatus of claim 11, wherein a first distance from a top surface of the first electrode to an interface between the lower light-emitting layer and the upper light-emitting layer is equal to or less than a second distance from a bottom surface of the second electrode to the interface between the lower light-emitting layer and the upper light-emitting layer.
 17. The apparatus of claim 16, wherein a ratio of the second distance to the first distance is in a range of 1.0 to 1.3.
 18. An organic light emitting display apparatus, comprising: a first electrode; a second electrode; a first light-emitting portion on the first electrode, the first light-emitting portion including a first light-emitting layer; a second light-emitting portion on the first light-emitting portion, the second light-emitting portion including a second light-emitting layer; and a third light-emitting portion on the second light-emitting portion, the third light-emitting portion including a third light-emitting layer, wherein the second light-emitting layer includes a first area and a second area, and a first distance from a top surface of the first electrode to the first area is equal to or less than a second distance from a bottom surface of the second electrode to the second area, and wherein the first light-emitting portion, the second light-emitting portion, and the third light-emitting portion is configured to emit white light having an X-axis coordinate value and a Y-axis coordinate value in the color coordinate system, and wherein a range of fluctuation of the X-axis coordinate value at each pixel position and a range of fluctuation of the Y-axis coordinate value at each pixel position are equal to or less than 0.015.
 19. The apparatus of claim 18, wherein the second light-emitting layer is configured to emit yellow-green light and a concentration of a dopant in the first area is greater than a concentration of a dopant in the second area.
 20. The apparatus of claim 18, wherein a ratio of the second distance to the first distance is in a range of 1.0 to 1.3.
 21. The apparatus of claim 18, wherein the Y-axis coordinate value in the color coordinate system is greater by 0.03 or more than the X-axis coordinate value in the color coordinate system.
 22. The apparatus of claim 18, wherein the X-axis coordinate value in a color coordinate system is equal to or greater than 0.29, and the Y-axis coordinate value in the color coordinate system is in a range of 0.32 to 0.45.
 23. The apparatus of claim 18, wherein the first light-emitting portion is configured to emit blue light, and the second light-emitting portion is configured to emit yellow-green light or mixed light of green and red, and the third light-emitting portion is configured to emit blue light. 